1. Field of the Invention
The present invention relates to a composition for inhibiting an increase of a blood sugar level or lowering a blood sugar level. More specifically, it relates to a composition for inhibiting an increase of a blood sugar level or lowering a blood sugar level, which composition contains extract components from Lagerstroemia Speciosa, Linn. or Pers. as a main component and has a specific content of corosolic acid.
2. Prior Art of the Invention
Lagerstroemia Speciosa, Linn. or Pers. comes under the loosestrife family of Myrtales and is generally called xe2x80x9cqueen""s crape myrtlexe2x80x9d as well, and it occurs widely in south east Asian areas including the Philippines, India, Malaysia, southern China and Australia. In the Philippines in particular, dry leaves and flowers of Lagerstroemia Speciosa, Linn. or Pers. are decoted and taken as a drink. This drink is also well known as a folk medicine against diabetes.
Leaves of Lagerstroemia Speciosa, Linn. or Pers. have received attention and an extract thereof has been analyzed for obtaining some components. It has been accordingly reported that corosolic acid is contained as one of the components and that the corosolic acid has been studied for its activity by using Ehrlich Ascites Tumour Cells to show that it is a substance which activates the mobility of grape sugar [Chem. Pharm. Bull. 41(12) 2129-2131 (1993)].
The above report is concerned with results of in vitro experiments and merely suggests results of first-stage discrimination test of anti-diabetes activities of corosolic acid.
JP-A-5-310587 discloses an anti-diabetes preparation containing, as an ingredient, a concentrated dry substance (Lagerstroemia Speciosa, Linn. or Pres. powder extract) obtained by extracting leaves of Lagerstroemia Speciosa, Linn. or Pers. in hot water or an organic solvent. The above preparation is an easily prepared and high-safety anti-diabetes preparation produced by taking out a water-soluble fraction and a lipid-soluble fraction from an extract of leaves of Lagerstroemia Speciosa, Linn. or Pers. and adjusting it to a dry extract. The above publication discloses a preferred embodiment in which the powder extract is diluted, e.g., in a concentration of 2% and taken as a drink, and the anti-diabetes activity thereof is confirmed by an animal experiment using mice diseased with diabetes.
As already described, dry leaves of Lagerstroemia Speciosa, Linn. or Pers. have been used as having an effect on the therapy of diabetes in folk medicine. However, it is not clearly known what component(s) of the leaves of Lagerstroemia Speciosa, Linn. or Pers. has/have human anti-diabetes activity. It is known that corosolic acid is contained as one component, while the activity thereof is a mere result of a study of the function to activate the mobility of grape sugar in an in vitro experiment using cells.
Further, there has been no specific clinical knowledge of component(s) of the extract of leaves of Lagerstroemia Speciosa, Linn. or Pers. which has/have activity in the therapy of human diabetes. Moreover, there has been found no knowledge obtained by studying a relationship between component(s) of the extract of leaves of Lagerstroemia Speciosa, Linn. or Pers. and an increase in a human blood sugar level.
The present inventor has therefore studied a relationship between component(s) of an extract of leaves of Lagerstroemia Speciosa, Linn. or Pers. and an increase or inhibition of an increase in human blood sugar level on the basis of clinical tests. When a composition which was a concentrated extract of leaves of Lagerstroemia Speciosa, Linn. or Pers. and which had a specific content of corosolic acid was administered to mild-case diabetes patients who had a fasting blood sugar level of slightly higher than approximately 110 mg/dl and who were insulin-non-dependent, it was found that an increase in blood sugar level was inhibited and that the blood sugar levels decreased on average.
According to studies by the present inventors, it has been also found that the composition which had a specific content of corosolic acid can be obtained by extracting, concentration and drying leaves of Lagerstroemia Speciosa, Linn. or Pers., under a specific condition.
According to the present invention, therefore, there is provided a composition for inhibiting an increase blood sugar level, which comprises, as a main component, a concentrate of a hot water or alcohol extract of leaves of Lagerstroemia Speciosa, Linn. or Pres. and has a corosolic acid content of 0.01 to 15 mg per 100 mg of the concentrate.
According to the present invention, further, there is provided a method of inhibiting an increase in a blood sugar level, which comprises orally administering the above composition to a patient who is expected to suffer an increase in blood sugar level from a normal blood sugar level.
Further, according to the present invention, there is provided a method of lowering a blood sugar level to a normal level, which comprises orally administering the above composition to a mild-case diabetes patient having a blood sugar level higher than a normal level to some extent or a serious diabetes patient having a high blood sugar level.
The present invention will be explained more specifically hereinafter.
Corosolic acid is one of triterpenoids having the following structural formula. 
It is considered that the activity of the composition of the present invention in inhibiting an increase in, or lowering, a human blood sugar level is caused by the interaction of a specific content of corosolic acid in the concentrate and extracted components of leaves of Lagerstroemia Speciosa, Linn. or Pers.
Leaves of Lagerstroemia Speciosa, Linn. or Pers. used as a raw material for the composition of the present invention refer to green leaves of Lagerstroemia Speciosa, Linn. or Pers. which occurs in the Philippines or some other areas or a dry product prepared by drying the same. The green leaves may be dried by leaving it in atmosphere, by air-drying or by forcible drying. Preferably, the drying is carried out by so-called toasted-drying until the leaves have a water content of 20% by weight or less, preferably 10% by weight or less, for preventing the growth of microorganisms and attaining storage stability.
Green leaves of Lagerstroemia Speciosa, Linn. or Pers. may be extracted as they are, while it is desirable to pulverize the dry leaves or cut them into pieces before the extraction.
The method and condition of extracting leaves of Lagerstroemia Speciosa, Linn. or Pers. in hot water or an alcohol and concentrating the extract are not specially limited, while there should be employed a method and a condition under which a resultant concentrate has a specific content of corosolic acid. That is, the concentrate preferably has a corosolic acid content of 0.01 to 15 mg per 100 mg of the concentrate (dry solid substance). The corosolic acid content per 100 mg of the concentrate is preferably 0.1 to 15 mg, more preferably 0.2 to 12 mg, particularly preferably 0.5 to 10 mg.
In the composition of the present invention, those components of the leaves of Lagerstroemia Speciosa, Linn. or Pers. which are other than corosolic acid also have an effect on the activity, and it is required to take account of components to be extracted and a concentrating method and condition with regard to other components. A preferred embodiment of a proper method and a proper condition will be apparent from an explanation to be given later.
Method 1
In this method, a pulverization product of dry leaves of Lagerstroemia Speciosa, Linn. or Pers. (raw material) added to ethanol or an ethanol aqueous solution (ethanol content 50 to 80% by weight) in an amount 5 to 20 times, preferably 8 to 10 times the weight of the raw material, and the mixture is refluxed under heat at a temperature between room temperature and 90xc2x0 C., preferably approximately between 50xc2x0 C. and 80xc2x0 C., for 30 minutes to 2 hours. The above extraction is repeated twice or three times. The resultant extract may be decolorized as required by adding 5 to 10% by weight, based on the raw material, of activated carbon. The decolorization is useful for expanding the use range of the composition of the present invention to foods, and the like. Then, the extract is filtered and concentrated at a temperature of 60xc2x0 C. or lower under reduced pressure to obtain a solid, and the solid is dried at a temperature between 50xc2x0 C. and 70xc2x0 C. under reduced pressure (higher reduction rate than that during the concentration). The thus-obtained solid is pulverized to obtain a powdery concentrate. The concentrate obtained by the above method has a specific content of corosolic acid and contains an effective amount of other components as well.
Method 2
This method is an extraction method using methanol or a methanol aqueous solution. In this method, the extraction is carried out in methanol or a methanol aqueous solution (methanol content 50 to 90% by weight) in an amount 3 to 20 times the weight of the raw material. The extraction procedure is preferably carried out at a temperature between room temperature and 65xc2x0 C. for 30 minutes to 2 hours. The number of times of the extraction procedure is not limited to once, and the extraction procedure may be carried out twice or more. The obtained extract is decolorized as required, and concentrated under the same conditions as those in the above method 1, whereby a solid can be obtained.
Method 3
This method 3 is an extraction method using hot water. There is used hot water in an amount 3 to 20 times the weight of the raw material, and the extraction is carried out at a temperature between 50xc2x0 C. and 90xc2x0 C., preferably between 60xc2x0 C. and 85xc2x0 C., for 30 minutes to 2 hours. Desirably, the concentration and drying after the extraction are carried out for a relatively short period of time since active components may be sometimes deteriorated when the concentrate is maintained at a high temperature for a long period of time. For this reason, it is advantageous to carry out the concentration and the drying under reduced pressure.
The above-explained methods 1 to 3 have been described for explaining basic methods and conditions, and these methods may be altered and/or combined as required. For example, the method 1 and the method 2 may be combined. Of the above methods 1 to 3, the methods 1 and 2 are preferred, and the method 1 is particularly preferred.
Function and Effect of the Composition of the Present Invention
When used as a preparation for inhibiting an increase in, or lowering, the blood sugar level, the composition of the present invention has the following advantages.
(a) It has been reported that conventional oral preparations for the therapy of diabetes such as a sulfonyl urea preparation, a biguanide preparation, an insulin resistant amelioration preparation, etc., causes side effects such as hepatopathy, disorder of digestive organs, nausea, vomitting, etc., while the composition of the present invention is free of these side effects.
(b) The above conventional preparations for the therapy of diabetes end their effects when the administration thereof is discontinued, while the composition of the present invention continues to have an effect and has a continuing effect like traditional Chinese medicine since the blood sugar level does not increase when its administration is discontinued.
(c) The composition of the present invention does not cause a decrease in the blood sugar level when people having a normal blood sugar level takes it.
(d) It is considered that the above advantages of the composition of the present invention are exhibited since corosolic acid contained in leaves of Lagerstroemia Speciosa, Linn. or Pers. activates grape sugar transportation even if its concentration is very low.
It is considered that intensification of the grape sugar transportation activity of corosolic acid in xe2x80x9cintaking of sugarxe2x80x9d and xe2x80x9cconversion of sugar to energyxe2x80x9d is a function different from that of conventional preparations for the therapy of diabetes.
(e) It is also assumed that the composition of the present invention has another activity in inhibiting the digestion and absorption of glucide by preventing the function of typical digestive enzyme of glucide. It is considered that the above activity is caused by the interaction of corosolic acid and other component(s) in the concentrated extract of leaves of Lagerstroemia Speciosa, Linn. or Pers.
The composition of the present invention can therefore inhibit an increase in a blood sugar level by orally administering it to patients who are expected to suffer an increase in blood sugar level from a normal blood sugar level. The above oral administration can be continued for a long period of time, and even if the composition of the present invention is continuedly taken for a long period of time, the blood sugar level comes to be lower than a normal blood sugar level in no case. Further, the oral administration causes no or almost no other harms or side effects.
Further, when orally administered to diabetes patients, the composition of the present invention can lower their blood sugar level to a normal level. The composition of the present invention can work on any one of mild-case patients having a blood sugar level higher than a normal blood sugar level to some extent and serious patients having a considerably higher blood sugar level.
When the composition of the present invention is orally administered, desirably, the dosage of the concentrate having a corosolic acid content of 0.01 to 15 mg per kg of a human body weight per day is 50 mg to 1,000 mg, preferably 70 mg to 800 mg. Specifically, the oral administration is preferably separated to twice or three times a day. Desirably, further, the oral administration of the composition of the present invention is conducted continuedly for at least one month, preferably for at least three months.
The composition of the present invention may have the prepartion form of a powder or granules, and it may also have the preparation form of a tablet such as pellets or an encapsulated preparation.